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Re: [PATCH v2 04/11] multifd: Count the number of bytes sent correctly
From: |
Chuang Xu |
Subject: |
Re: [PATCH v2 04/11] multifd: Count the number of bytes sent correctly |
Date: |
Fri, 16 Jun 2023 03:53:10 -0500 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 |
Hi,Juan,
On 2023/1/30 下午4:09, Juan Quintela wrote:
> Current code asumes that all pages are whole. That is not true for
> example for compression already. Fix it for creating a new field
> ->sent_bytes that includes it.
>
> All ram_counters are used only from the migration thread, so we have
> two options:
> - put a mutex and fill everything when we sent it (not only
> ram_counters, also qemu_file->xfer_bytes).
> - Create a local variable that implements how much has been sent
> through each channel. And when we push another packet, we "add" the
> previous stats.
>
> I choose two due to less changes overall. On the previous code we
> increase transferred and then we sent. Current code goes the other
> way around. It sents the data, and after the fact, it updates the
> counters. Notice that each channel can have a maximum of half a
> megabyte of data without counting, so it is not very important.
>
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
> migration/multifd.h | 2 ++
> migration/multifd.c | 6 ++++--
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/migration/multifd.h b/migration/multifd.h
> index e2802a9ce2..36f899c56f 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -102,6 +102,8 @@ typedef struct {
> uint32_t flags;
> /* global number of generated multifd packets */
> uint64_t packet_num;
> + /* How many bytes have we sent on the last packet */
> + uint64_t sent_bytes;
> /* thread has work to do */
> int pending_job;
> /* array of pages to sent.
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 61cafe4c76..cd26b2fda9 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -394,7 +394,6 @@ static int multifd_send_pages(QEMUFile *f)
> static int next_channel;
> MultiFDSendParams *p = NULL; /* make happy gcc */
> MultiFDPages_t *pages = multifd_send_state->pages;
> - uint64_t transferred;
>
> if (qatomic_read(&multifd_send_state->exiting)) {
> return -1;
> @@ -429,7 +428,8 @@ static int multifd_send_pages(QEMUFile *f)
> p->packet_num = multifd_send_state->packet_num++;
> multifd_send_state->pages = p->pages;
> p->pages = pages;
> - transferred = ((uint64_t) pages->num) * p->page_size + p->packet_len;
> + uint64_t transferred = p->sent_bytes;
> + p->sent_bytes = 0;
> qemu_file_acct_rate_limit(f, transferred);
> qemu_mutex_unlock(&p->mutex);
> stat64_add(&ram_atomic_counters.multifd_bytes, transferred);
> @@ -719,6 +719,8 @@ static void *multifd_send_thread(void *opaque)
> }
>
> qemu_mutex_lock(&p->mutex);
> + p->sent_bytes += p->packet_len;
> + p->sent_bytes += p->next_packet_size;
Consider a scenario where some normal pages are transmitted in the first round,
followed by several consecutive rounds of zero pages. When zero pages
are transmitted,
next_packet_size of first round is still incorrectly added to
sent_bytes. If we set a rate
limiting for dirty page transmission, the transmission performance of
multi zero check
will degrade.
Maybe we should set next_packet_size to 0 in multifd_send_pages()?
> p->pending_job--;
> qemu_mutex_unlock(&p->mutex);
>
- Re: [PATCH v2 04/11] multifd: Count the number of bytes sent correctly,
Chuang Xu <=